The field of this invention relates to the welding of separate metallic cylindrical tubular elements by the gas shielded tungsten electro-arc welding process. More particularly, this invention relates to the welding apparatus to automatically efficiently produce an extremely strong weld between piping sections.
Although the structure of this invention is designed primarily to weld piping sections of enlarged diameters, such as thirty inches in diameter, it is considered to be within the scope of this invention to use the structure and method of this invention on pipes smaller than thirty inches in diameter and also pipes larger than thirty inches in diameter. The inherent difficulty encountered in larger diametered pipes is that the pipe itself cannot be turned or rotated during the welding operation. This requires that the welding torches themselves to be rotated about the pipe. This means that gravity is a primary consideration in producing a satisfactory weld. The effect of gravity is readily apparent when it is considered that at the upper surface of the pipe the gravity has a tendency to draw the molten weld material toward the inside of the pipe while at the bottom of the pipe the gravity has the effect of having a tendency of pulling the molten weld material in exactly the opposite direction.
A desirable type of weld is a weld bead which is slightly raised on both the inside and outside surface of the pipe. Satisfactory penetration of the heat energy must occur to melt the edges of the piping and then with the addition of the filler wire completely fill the welding groove with an intermolecular bond occurring between the melted filler wire and the metallic material of the piping itself. Without satisfactory heat penetration into the piping, a poor quality weld will be produced and the resultantly formed pipe will be inherently weakened in this spot and a break can occur. The problem of welding larger diametered pipes is that gravity does have a definite effect on the welding process, since the welding material, for a short period of time, does become liquid and has a tendency to flow in a downward direction toward the earth. In any automatic welding process, compensation must be provided for gravity in order to produce a satisfactory weld at the upper surface of the piping as well as at the lower surface of the piping. Heretofore, there has not been sufficient emphasis placed on the effect of gravity, and the devices which have been designed to weld such larger diametered piping in a semiautomatic manner require a manual adjustment in order to compensate for the effect of gravity. The result is not a completely automatic welding process but a method which requires manual adjustment in order to compensate for gravity. This manual adjustment inherently introduces the possibility of human error which could be avoided by a completely automatic system.
The structure of this invention is found to be of particular utility in the area of constructing off-shore oil and gas pipeline. This pipeline is welded together on barges and then the pipeline is dispensed to be positioned at the bottom of the body of water. At the present time, there are four welders used to make a single three hundred and sixty degree weld pass in assembling of this off-shore pipeline. There are normally five or six separate welding stations on each barge and at each welding station there are four welders. In using the automatic welding apparatus of the subject invention, there would only be required to have a single welder per welding station.